1. Field of Invention
The present invention relates to a photomask pattern. More particularly, the present invention relates to a high-resolution photomask pattern.
2. Description of Related Art
In recent years, the semiconductor industry has been in favor of producing miniature circuit devices. One of the most critical aspects in miniaturizing circuit devices in semiconductor process is photolithography. The critical dimension of any related structure of a semiconductor device such as various thin films and patterns depends on the resolution in the photolithographic process. Since the accuracy of the photomask pattern transfer directly affects the tolerance of critical dimensions on a chip, and increasing the resolution of the photomask is very important.
To increase the resolution of photomask pattern, two major methods are deployed. One method is to use a binary chrome mask together with an off-axis illumination (OAI) to serve as a light source for the photo-exposure. Alternatively, an attenuated phase-shift mask (APSM) together with an off-axis illumination (OAI) is used to perform the photo-exposure process. The concept behind the attenuated phase-shift mask method is to add suitable material to the pattern area so that there is a phase difference of 180° between the patterned and non-patterned area and that the mask has a sufficiently high degree of transparency for high productivity.
However, the aforementioned photolithographic processes can hardly keep up with the decreasing critical dimensions demanded for miniaturized products so that the uniformity of critical dimensions is varied.